The present invention relates to an apparatus for administering oxygen on demand to a patient. More particularly, the present invention relates to an apparatus having a sensor for detecting a patient's inhalation cycle and triggering release of a valve to deliver oxygen to a patient.
Patients having reduced lung function or suffering from pulmonary diseases such as emphysema, bronchitis, and asthma, are commonly treated by delivery of supplemental oxygen. The supplemental oxygen is typically delivered to a patient through a face mask or attached nasal cannula. Currently, for most patients this oxygen is delivered at a determinable constant rate, with oxygen continuously flowing without regard to the breathing cycle of the patient. As will be appreciated, this continuous flow results in substantial waste of oxygen delivered during breath exhalation of the patient. The waste of oxygen is particularly detrimental for patients relying on portable devices that have a limited storage capacity, requiring frequent oxygen recharges that can limit mobility and independence of patients.
To overcome this limitation, devices that deliver oxygen on demand have been proposed. For example, U.S. Pat. No. 4,054,133 to Myers describes a pneumatic control system for regulating the flow of oxygen to a patient. The described system delivers oxygen on demand, and is triggered by the pressure differential between inhalation and exhalation pressure as measured in the nasal cavity. Similarly, U.S. Pat. No. 4,575,,042 to Grimland et al. describes a pneumatically amplified valve that again requires both a sensing tube and an output tube for operation. However, use of such devices is not always convenient, since large, dual lumen cannula are typically required for operation of the device.
As an alternative to the dual lumen, fully pneumatic triggering system, it is possible to use electronic pressure or gas flow sensors to trigger an oxygen administration device. Such electronic sensors advantageously use widely available single lumen cannulas. For example, U.S. Pat. No. 5,005,570 to Perkins describes a device which temporarily stores a premetered, single dose of oxygen, and dispenses the oxygen in synchronization with a patient's inhalation cycle. An electronic sensor is used to produce a signal with the onset of inhalation that delivers electric power to open a valve. This sensor controlled, intermittent opening of the valve allows flow of oxygen through a single cannula to the patient. However, practical application can be limited because of the substantial power requirements for valve operation. Typically, a large solenoid operated valve is required to ensure fast, high volume delivery of oxygen to the patient. These valves require substantial direct current power, and oxygen delivery device manufacturers often must balance short operational battery life against the weight and bulk of additional batteries when designing portable systems.
The present invention overcomes the limitations inherent in dual lumen systems, and the short battery life of the foregoing electronically controlled valve system, by provision of a load activated oxygen delivery system configured to deliver oxygen from an oxygen source to a patient through a single cannula in response to patient inhalation. The oxygen delivery system includes a regulator assembly connectable to the oxygen source, and a main body assembly configured to define a precharge chamber for holding oxygen. The precharge chamber has an inlet and an outlet, with the inlet connected to the regulator assembly. In preferred embodiments, volume of the precharge chamber can be adjusted.
A demand body assembly is attached in fluid communication to the precharge chamber. The demand body assembly is configured to define a slave chamber in fluid communication with the single cannula and an actuating chamber in fluid communication with the regulator. The slave chamber is separated from an actuating chamber by a diaphragm, with the diaphragm positioned to seal the precharge chamber outlet during patient exhalation. The diaphragm moves to an unsealed position during patient inhalation to allow oxygen in the precharge chamber to flow through the precharge chamber outlet into the slave chamber, thereby passing out through the single cannula to the patient.
The present invention does not require an energetically expensive electronic valve or a separate pneumatic line devoted solely to sensing inhalation. Instead, a solenoid assembly or other electronic valve system is positioned in fluid communication with the actuating chamber to open the flow path between the outlet of the precharge chamber and the slave chamber. In effect, the present invention utilizes the power advantage of a pneumatic system without requiring the separate pneumatic triggering line.
The operation cycle of the present invention is initiated by a patient's inhalation. The pressure drop is sensed in the single cannula and the solenoid assembly is energized to open a movable valve. As oxygen pressure in the actuating chamber drops below oxygen pressure in the slave chamber, the pressure differential causes the diaphragm to move away from its sealed position over the precharge chamber outlet. Oxygen quickly flows out from the now unsealed precharge chamber outlet, providing a burst of oxygen in excess of the prescribed continuous flow oxygen rate from the precharge chamber to the patient. This burst of oxygen is necessary to overcome high levels of oxygen that collect in the vicinity of the patient's nasal cavity in "continuous flow" oxygen delivery, which is used to define the patient's prescription flow rate.
In preferred embodiments the flow rate of oxygen can be controlled with the aid of a rotor connected by drive pins to the demand body assembly and positioned in the main body assembly for rotation to a plurality of indexed positions between the regulator assembly and the precharge chamber. The rotor has a calibrated flow path defined therethrough at each indexed position for controlling oxygen flow into the precharge chamber.
In addition to the control of rate and volume of oxygen delivery possible with adjustment to the precharge chamber volume and rotor position, it is also contemplated to employ timing circuits that deactivate the solenoid assembly to close the movable valve prior to completion of patient inhalation. Such a timing circuit prevents wastage of oxygen not deliverable to the lungs before completion of inhalation exhalation by the patient.
Advantageously, the present invention provides an oxygen delivery system that has low power consumption and an extended battery life. Current draw from both the pressure sensor and the valve controlling pressure in the actuating chamber is minimal compared to those devices which directly operate large valves to control oxygen flow.
Another advantage of the present invention is the increased control of oxygen delivery rate, volume, and timing. Adjustments can be made individually and separately to the timing circuit, the volume of the precharge chamber, and the rotor position to provide the best combination that effectively delivers sufficient oxygen to a patient with minimal oxygen wastage.
Additional objects, features, and advantages of the present invention will be apparent upon consideration of the following detailed description and accompanying drawings.